Over the years there has been a tremendous growth in the use of plastics to produce a variety of consumer goods and industrial products. Such materials lend themselves to different production methods and techniques. Frequently the production method is dictated by the particular article to be manufactured. For example, production of large plastic articles is accomplished for the most part by rotational molding, or at least the rotational molding process finds particular applicability in the production of large hollow products. Rotational molding is accomplished, for example, by supplying to a mold a measured amount of powdered thermoplastic moldable material and rotating the mold while heating it to fuse the thermoplastic powder and then cooling the mold to cause the molded article to solidify. Usually the mold is closed and is rotated around more than one axis, for example two axes at right angles, to distribute the powdered material throughout the mold to produce a completely closed article.
Ethylene polymers (homopolymers, copolymers, terpolymers, etc.) are used in rotational molding applications as well as numerous other applications. In many instances the ethylene polymers are compounded with various crosslinking agents (such as organic peroxides) which enhance the physical properties of the polymer, e.g. impact strength. Flame retardant systems comprised of a halogenated organic compound and an oxide of antimony are added to ethylene polymers to increase the resistance of the polymer to combustion. The combination of the peroxide crosslinking agent and the flame retardant system causes the undesirable formation of bubbles in the polymer. The bubbles are undesirable since they can be relatively large, e.g., up to about 1/2 inch in diameter or more, can extend to each surface of the walls and can terminate in pin holes or larger openings. As a result, articles produced from this type of polymer are unsuitable for many uses. Also, the appearance and the impact strength of the molded articles can be adversely affected by a large bubble population.